Process for dispersing refractory metal oxides in other metals



United States Patent 3,382,062 PROCESS FOR DISPERSING REFRACTORY METALOXIDES IN OTHER METALS Dale M. Hiller, Wilmington, Del., assignor, bymesne assignments, to Fansteel Metallurgical Corporation, a corporationof New York No Drawing. Filed Oct. 15, 1964, Ser. No. 404,154 4 Claims.(Cl. 75-.5)

ABSTRACT OF THE DISCLOSURE Power alloys of modybdenum with iron, cobalt,or chromium with or without copper, containing dispersed refractoryoxides such as thoria, are made by precipitating a particulate solidcontaining the alloy constituents other than molybdenum, dispersing saidsolid in aqueous ammonium molybdate solution at pH 5.5 to 8.5 to depositmolybdenum-containing compound on it, calcining said product at 100 to550 C., and reducing the calcined material at 450 to 1200 C.

This invention relates to processes for producing an alloy in powderform, said alloy having dispersed therein very fine particles of arefractory metal oxide and comprising a metal matrix consisting of (A)molybdenum and (B) at least one other metallic component selected fromthe group consisting of iron, cobalt, nickel, chromium, at least onemetal of these four with tungsten, and at least one metal of saidfourwith copper; and in such processes the invention is moreparticularly directed to the steps comprising (1) preparing aparticulate solid comprising a compound of each metal other thanmolybdenum to be present in the final alloy, in which particulate solidthere is so dispersed as to be inseparable by mechanical means, from0.05 to by volume of refractory oxide particles having an averageparticle size of 2 to 500 millimicrons and a free energy of formation at1000 C. of at least 95 kcaL/gram atom of oxygen; (2) dispersing saiddispersion-modified particulate solid in an aqueous ammonium molybdatesolution having a pH in the range of 5.5 to 8.5,- in an amountsubstantially exceeding the solubility of said solid in said solution,and maintaining the pH in that range until a molybdenum-containingcoating is deposited on the surface of the particulate solid: (3)separating the coated solid from the solution and calcining it in thetemperature range of 100 to 550 C.; and (4) heating the calcined productin the temperature range of 450 to 1200 C. in

contact with a reducing agent selected from the group consisting ofhydrogen, carbon, carbon monoxide and hydrocarbon gases, whereby thedispersion-modified particulate solid and its molybdenum-containingcoating are reduced to ther component metals and these metals arealloyed with each other. The dispersed refractory oxides having a freeenergy of formation at 1000 C. of at least 95 kcal./gram atom of oxygenare not reduced under these conditions, and remain as a dispersoid inthe alloy product.

Molybdenum is a valuable alloying element for iron, cobalt, nickel, andchromium, forming with these metals alloys which have high strength atvery high temperatures. When dispersion-modified alloys of these metalsare prepared by prior art methods, for example by milling of dry powdermixtures, ditficulty is encountered in obtaining powders of completelyhomogeneous, uniform composition. This difficulty persists even when thepowders are prepared by precipitation methods, as by precipitatingoxidic compounds of the alloying metals and reducing the oxides withhydrogen or other reducing agents.

3,382,062 Patented May 7, 1968 Moreover, in precipitation methodsheretofore known, undesirable impurities are often introduced, theremoval of which poses special problems.

Other preparation methods, as, for example, Alexande r et al. US. Patent2,972,529, have been described which have attempted to overcome thedifficulty of impurity of the alloy product by restricting the choice ofreagents to those whose by-products may be completely removed bysubsequent calcination. However, the chemical composition, specificallythe molybdenum content of the resultant alloy, remains a problem, i.e.the molybdenum content is subject to wide and unpredictablefluctuations.

Now according to the present invention, it has been found that thesolution to the problem of molybdenum homogenization in itsdispersion-modified alloys with iron, cobalt, nickel and chromium liesin processes wherein the oxidic compounds of iron, cobalt, nickel, andchromium or their mixtures, and of these with tungsten or copper, arefirst precipitated as a dispersion-modified particulate solid, andthereafter the oxidic molybdenum compound is deposited on thisprecipitate from an aqueous ammonium molybdate solution at a carefullycontrolled pH, followed by calcination and reduction of the product. Thepresent invention provides processes whereby molybdenum-bearing,dispersion-modified alloys having closely controlled composition areproduced, making it possible to duplicate alloy compositions from batchto batch within very specific limits, the molybdenum content of theproduct being controllable to, say, :0.2%. The invention also providesprocesses by which the impurity content of the alloys is kept to aminimum, thereby producing alloys of improved metallurgicalcharacteristics. Therefore the present invention simultaneously solvesthe problems of inhomogeneity, impurity, and unpredictable fluctuationsin chemical composition of dis persion-modified alloys.

The particulate solid which is to act as a substrate for the subsequentdeposition of molybdenum values is selected from the group consisting ofcompounds of one or more of the metals iron, cobalt, nickel andchromium, and'compounds of at least one of these with tungsten or withcopper-that is, it must contain a compound of each metal other thanmolybdenum which is to be present in the final alloy. There must bedispersed in the particulate solid matrix-metal substrate andmechanically inseparable therefrom, the refractory-oxide fillerparticles which serve to enhance the mechanical properties of the alloyproducts of this invention. The particulate, dispersionmodified solid isfurther characterized in that the particulate solid should not dissolveto an extent of more than 30 grams of metal per liter in aqueousammonium molybdate solution at a pH of 5.5 to 8.5, and must be reducibleto its component metals at a temperature in the range of 450 to 1200 C.after having been calcined at to 550 C. The presence of each of thesecharacteristics can be determined quite independently of the use of thematerial in the process of the present invention.

The dispersion-modified particulate solid can be precipitated as anoxidic, i. e. oxygen-containing, compound with refractory-oxide fillerbeing present. Thus the solid can be an oxide, hydroxide, hydrous oxide,oxycarbonate, or hydroxycarbonate of the metal or metals other thanmolybdenum to be present in the final alloy. One may precipitate theoxidic metal compound from any soluble salt thereof. The nitrate ispreferred, but chlorides, sulfates, or acetates are also useful. Amongthe preferred starting materials are ferric nitrate, cobalt nitrate, andnickel nitrate.

A single refractory filler may be present, or there may be more than onefiller present. The refractory oxide filler particles which serve tomodify the properties, and particularly the strength, of the alloyproducts of this invention comprise relatively non-reducible oxides;that is, oxides which are not reduced to the corresponding metal underconditions whereby the oxidic precursors of the matrix alloy areconverted to the metallic state. Such oxides can be used in the oxideform as starting materials, or they can be formed during the operationof the process by heating an oxide-forming material. Thus, themetal-oxygen-containing material from which the filler particles may bederived can be a metal oxide, hydrous oxide, carbonate, oxalate, or ingeneral any compound which upon heating to constant weight at 1500Cforms a refractory metal oxide. Typical oxides which are useful asfiller particles include alumina, zirconia, titania, magnesia, hafniaand various other oxides, including especially thoria. A listing ofrefractory oxides which meet the requirements of this invention will befound in U.S. Patent 2,972,529, column 3, lines 21 to 45, issued to G.B.Alexander et al., Feb. 21, 1961.

Precipitation of the dispersion-modified particulate solid can beaccomplished conveniently by adding suitable solutions of the matrixmetal salt or salts to an aqueous alkaline solution while maintainingthe pH above7. Alternatively, the matrix metal salt solution andsuitable solution or aquasol of the refractory oxide-forming materialcan be added simultaneously but separately to a heel of water. It ispreferred, however, not to coagulate or gel the colloidal dispersion ofthe filler particles. Coagulation and gelation are avoided by operatingwith dilute solutions, or by simultaneously adding solutions ordispersions of the filler and the alloying metal salt or salts to a heelof water as described above.

After the dispersion-modified oxidic compounds of the metal or metalsother than molybdenum having been precipitated, it is desirable toremove by-product salts formed during the precipitation reaction bywashing the precipitate. Since one generally uses an alkaline materialsuch as sodium hydroxide, potassium hydroxide, lithium hydroxide,ammonium or tetramethylammonium hydroxide, ammonium carbonate or sodiumcarbonate to effect precipitation of the dispersion-modified particulatesolid, salts such as sodium nitrate, ammonium nitrate, or potassiumnitrate will be formed. These must be removed completely from aprecipitated substrate material so that they will not interfere in thefinal molybdenum-modified alloy product.

One of the advantages of using the salts of nitric acid in combinationwith aqueous ammonia in the precipitation of the dispersion-modifiedparticulate solid which is to be the substrate material for themolybdenum precipitation is that ammonium nitrate is volatile atrelatively low temperatures, and therefore easily removed during thesubsequent heating of the substrate material. However, the tendency ofmany metals such as, for example, cobalt and nickel to form aminecomplexes, is a complicating reaction in the precipitation step.Although these undesirable side reactions can be avoided to a largeextent by carefully controlling the pH during the precipitation of thesubstrate, the precipitated product should be thoroughly washed in orderto remove all possible impurities therefrom.

In a preferred embodiment of the invention, the particulate solidcomprises hydrous oxides of filler particles and is prepared bycoprecipitation of the alloying metal compounds and hydrous oxides ofthe filler particles, especially hydrous thoria, by mixing solutions ofthe alloying metal compounds, thorium nitrate, and aqueous ammoniumcarbonate. The carbonate-hydrous oxide substrate so obtained isthoroughly washed before being treated further to deposit themolybdenum-bearing coating thereon.

Colloidal metal oxide aquasols contain particles in the most desirablestate of subdivision and size range and thus are an advantageous formfor the introduction of refractory oxide-producing materials in thealloy processes of this invention. In alloys comprising thoria as arefractory oxide filler, for example, a preferred method of addition isto add a thoria sol prepared by calcining thorium oxalate at 550C. anddispersing the resulting thoria in aqueous thorium nitrate solution.

In operation of a preferred embodiment of the invention, therefore,molybdenum values can be deposited on a substrate material which maycontain either embedded filler particles, or may have associated with ita metaloxygen-containing composition which upon subsequent heating formrefractory-oxide particles.

The relative amounts of the component metal compounds, and fillerparticles, are varied depending on the composition desired in thefinished alloyed product. A preferred level is from 0.5 to 10% by volumeof refractory oxide particles in the alloy product. An even morepreferred level is from 1 to 5% by volume. The percentage will bedependent to some extent upon the size of the particles, which in apreferred product may vary from, say, 5 to 150 millimicrons in averagediameter. The preferred level of 0.5 to 10% by volume, and the morepreferred range 1 to 5%, is based on the filler particles of about 25 maverage diameter in the final molybdenumbearing dispersion-modifiedalloyed product.

In a specifically preferred embodiment of this invention, a substrateupon which molybdenum values are deposited comprises nickel carbonate inwhich there is dispersed submicron size thoria. Although the compositionof the final nickel-molybdenum-thoria alloy may vary within quite wideranges of, say, 1 to 20% molybdenum and 0.05 to 10% thoria, a preferredcomposition in the final product is nickel10% by weight molybdenum-- 2%by volume thoria. Particular advantage is gained in an alloy of this, orof similar composition prepared by the process of this invention, inthat no high temperature heat treatment is required to effect alloyingof the metal components, and undesirable growth of refractory oxideparticles is thus avoided.

The use of ammonium molybdate as a source of the molybdenum-containingcoating for the substrate is particularly advantageous in that no solidimpurity ions are added to the slurry or to the circulated liquor to bepicked up on the substrate along with the molybdenum values. Theammonium ion is readily volatilized during subsequent heating prior toreduction. To deposit the molybdenum values uniformly upon the substratematerial, the pH of the slurry, i.e. of the ammonium molybdate solution,should be adjusted to a value in the range of 5.5 to 8.5 and maintainedat the chosen value until the molybdenumcontaining coating is deposited.A preferred pH value is 6.5. To adjust the pH to these values andmaintain the pH value at the desired point, acidification of the slurryis necessary and nitric acid is preferred as the acidifying agent. As inthe case of ammonium molybdate solution, nitric acid introduces noforeign ions which cannot be removed by subsequent calcination withoutwashing of the molybdenum-treated substrate material. The pH duringdeposition of the molybdenum values is held close to 6.5 to minimize inthe supernatent solution the total concentration of molybdate and ofredissolved metal ions from the substrate.

The deposition of molybdenum values upon the substrate material is notinstantaneous; normally the deposition requires 2 to 4 hours to reach asteady state. Longer times of treatment may be required if higher levelsof molybdenum deposition are desired; also longer times may be necessaryif a pH of higher than 6.5 is maintained in the liquor. The equilibriumdistribution of molybdate between the solid phase and the solution willdiiier for substrates of varying compositions and methods of preparationand can be determined experimentally in each case. In each instance,however, conditions of time and pH will be found experimentally whichwill permit transfer of more than of the molybdate to the solid phase.Once a type of substrate has been characterized and the preferableprocedure determined, the behavior is quite reproducible and materialcan be very satisfactorily duplicated from batch to batch.

After deposition of the molybdenum values has been accomplished, thesolids are dewatered, usually by filtration but it is preferred not towash the cake at this point because the amount of molybdate removed bywashing is difficult to predict or control. Since the foreign ions introduced into the slurry are removed by calcination, the product obtainedis of satisfactory quality without a washing step.

The dewatered particulate solid with its molybdenumcontaining coating isdried and calcined at a temperature of from 100 to 550 C. to yield anintimate mixture of pure oxides. Ordinarily, heating at 100 C. is notthought of as calcination, but here dehydration of some hydroxides tooxides is effected. To effect complete calcination, however, thetemperature is ordinarily carried well above 100 C. Higher temperaturesthan 550 C., on the other hand, are generally undesirable because theyare more expensive and tend to sinter the oxide and retard thesubsequent reduction of the oxide or oxides to metal. Also, highertemperatures tend to volatilize some of the oxides, as for example M00or W0 The molybdenum-treated substrate material, which has been calcinedat not over 550 C., is then pulverized, suitably in an impact mill suchas a hammer mill, to provide a powder having maximum available surfacefor the subsequent step of reduction of the metal oxides to metal.

The pulverized oxides are next reduced at a temperature in the range of450 to 1200 C. in contact with a reducing agent selected from the groupconsisting of hydrogen, carbon, carbon monoxide, and hydrocarbon gases,whereby the particulate solid and its molybdenum-containing coating arereduced to their component metals and these metals are alloyed with eachother. Preferably such reduction is carried out in a flowing stream or"reducing gas until the dew point of the effluent gas drops to 50 C.Although hydrogen is the preferred agent for most of the metals, otherreducing agents may be used instead of, or in combination with,hydrogen. The hydrocarbon gas may be methane or a higher hydrocarbon.

Whatever reducing agent or combination of reducing agents is used, it isimportant that the temperature during reduction be carefully controlledto avoid premature sintering of the product, which would result inentrapped, unreduced areas of metal oxide. Also, high temperatures areto be avoided before complete reduction of the matrix material iseffected, so that no reaction may take place between the reduciblecompounds of the metal matrix and the refractory oxide particles. Oneway to avoid premature sintering is to place the molybdenum-treatedsubstrate material in a furnace at a controlled temperature and add thereducing gas slowly so that sintering is avoided as reduction takesplace. In such a method of operation, the reduction reaction will notproceed so rapidly that large amounts of heat are liberated and thetemperature of the furnace thus uncontrollably increased. When areducing gas, or mixture of reducing gases, is used, it may be dilutedif desired with an inert gas such as argon to reduce the rate ofreaction and avoid hot spots and local sintering.

After reduction is complete, the reactor is cooled to room temperature,purged with an inert gas, and the product discharged. In the productthus obtained, the molybdenum values, and the tiller particles ifpresent, are distributed uniformly throughout the product.

Although no high-temperature treatments are necessary to alloy themolybdenum with other metal or metals which are present in thesubstrate, it may be found desirable for other reasons to heat thereduced product to an elevated temperature before subjecting it tofurther metallurgical treatments. By such heat treatment, any tendencyof the powdered alloy product to reoxidize in air is diminished becausesuch high-temperature treatment reduces the specific surface of thepowdered alloy product. Also, it will be realized that the temperatureat which a particular reduction reaction is carried out and thetemperature of any subsequent heat treatment will vary with thecomposition of the substrate. Thus substrate materials comprisingchromium and tungsten, for example, can be reduced and heat treated attemperatures higher than those used to reduce and heat treat substratematerials comprising, say, iron and copper. The time and temperature ofreduction and subsequent heat treating will be in part determined by thevolume loading of the filler in the alloy product and thegsize of thefiller particles. In any case, it is preferred to maintain thetemperature for both reduction and subsequent heat treatment at a pointnot higher than 50 C. below the melting point of the substrate metal oralloy.

In the foregoing description of this invention, reference has beenmade-repeatedly to refractory oxide filler particles. These areparticles which are not reducible under the conditions of reductioneffective on the matrix metals the particles serving to increase thestrength of the final alloy product. Designating such particles asfillers is not meant to indicate that they are inert extenders ordiluents; rather, they are effective constituents of the products of theinvention and products including them are a preferred embodimentthereof.

The invention will be better understood by reference to the followingexamples, which illustrate preferred embodiments thereof but are not tobe construed as limiting except as denoted in the appended claims. Allparts are by weight unless otherwise indicated.

Example 1 In this example the particulate solid starting material uponwhich molybdenum was deposited comprised nickel carbonate in which wasdispersed thoria of fine particle size. The particulate solid wasprepared by mixing 3-molar solutions of (1) nickel nitrate, Ni(NO and(2) ammonium carbonate, (NH CO in the presence of (3) a colloidaldispersion of 1% thoria stabilized by the addition of thorium nitrate,Th(NO The mean particle diameter of the thoria was 11 millimicrons (rm)and the molar proportion of Th(NO to ThO was 15:100. Mixing of thesolutions was effected by simultaneously introducing at separate inletsinto a pipeline mixer the solutions of nickel nitrate, ammoniumcarbonate, and thorium nitrate-thoria dispersion, with vigorousagitation in the reactor. Upon mixing of these materials, solidsprecipitated, with the thoria uniformly dispersed throughout theprecipitate. The nickel-to-thoria weight ratio in the precipitate was97.8:2.2. The final pH of the slurry after precipitation of thenickel-thoria solids was 7.0.

The slurry thus obtained was filtered in a filter press, and the filtercake was thoroughly washed with demineralized water. The washed solidswere repulped with vigorous agiLation in demineralized water to a slurryof 219 g. per liter, calculated on the nickel content. The total volumeof this slurry was 282.1 liters. While the repulped slurry was beingagitated, 41.1 liters of an ammonium molybdate solution containing 250grams of (NH Mo O .4H O per liter was added. This calculated to aMo/(Mo-l-Ni) content of 8.9%. After the addition of the ammoniummolybdatc solution, the slurry had a pH of 7.65. To adjust the pH to thedesired 6.5 value, addition of concentrated nitric acid was begun from aseparatory funnel, and 6.75 liters of acid were added over a period of0.8 hours. The pH of the slurry was now 7.00. Agitation and addition ofacid were continued for an additional 3 hour period, during which timean additional 9.80 liters of nitric acid were added. The pH of theslurry was now 6.50, and over a period of an hour with constantagitation, the pH remained unchanged.

The acidified slurry was then pumped to a filter press, and the presscake discharged into trays. The cake was dried and calcined at atemperature held to not over 550 C. for a period of 16 hours to yield amixture of pure oxides. The calcined cake was cooled and pulverized in ahammer mill.

The brown pulverized oxide thus obtained was charged in trays to areduction reactor. Commercially pure electrolytic hydrogen wascirculated over the oxide and the temperature was raised to 450 C.Reduction at this temperature was continued until the dew point of theeffiuent hydrogen dropped to 30 C. The oxides were then heated to 600 C.while the flow of hydrogen was continued, and the reduction wascontinued until the dew point dropped to 50 C. at which point thereduction was considered to be completed. The metal powder was heated at1000 to 1050 C. in hydrogen for an additional 3 hours time, was cooledto ambient temperature, the reactor purged with argon and opened to theair. The resulting metallic powder weighed 56.3 kg. and its propertieswere found to be as follows: thoria content 1.95%, Mo/(Mo-l-Ni) 8.26%;surface area 0.600 square meters per gram; and surface oxygen 0.131%.

To test the metallurgical properties of the material thus prepared, aportion of the powder was pressed into a 2" diameter by 2" long billetusing a hydrostatic pressure of 40,000 p.s.i. The compressed billet wasencased in a can, sintered in hydrogen for 1 /2 hours at 900 F. (480 C.)and then heated at 1650 F. (90 C.) for 2 /2 hours. The billet wasevacuated while being cooled to room temperature and then sealed in thecan, while under vacuum. The canned billet was extruded at an extrusionratio of 10:1 at a temperature of 910 C., cooled and decanted.

Examination of the as-extruded billet at 500x under the light microscopeand at 50,000 under the electron microscope showed no islands orstringers of thoria to be present. The extruded bar was cold worked to a50% reduction in cross-sectional area and tested for mechanicalproperties. The properties are listed in Table 1 below.

TABLE 1 [Mechanical Properties of Ni-8.26% M1.95% 'IhOr Alloy] 1,200 F.(650 C.) 2,000 F. (1,090 C.)

Properties Ultimate tensile strength (13.5.1.) 65, 000 17,000 Reductionin area (percent) 25 5. 3 Elongation (percent) 8 5. 2 Stress-torupturelife at 7,000 p.S.i. (hr.) .0

Example 2 Using the procedure of Example 1 for the precipitation ofnickel carbonate-thoria press cake, a 22.75 kg. lot of this particulatesolid starting material was prepared. This material contained 4.54 kg.of nickel values, and 102 grams thoria. The press cake was repulped in a60-liter container by vigorous agitation in 13.65 liters ofdemineralized water.

The slurry thus formed was treated with 11.05 liters of ammoniummolybdate solution at 250 grams molybdate per liter. Themolybdate-treated slurry was acidified by the addition of concentratednitric acid. A pH value of 6.5 was reached when the slurry had been acidtreated over a period of 1.5 hours. The pH was held at 6.5 by continuingaddition of nitric acid for 2 hours additional and the slurry was thenfiltered. The filtrate volume was 25.1 liters and contained 431 grams ofmolybdenum and 457 grams of nickel. This represents a 71.3% yield on themolybdenum values and a 90% yield on the nickel values in the slurry.

The press cake was dried, calcined, pulverized and reduced according tothe procedure of Example 1. By this process there was produced 5.05 kg.of nickel-molybdenum-thoria alloy powder containing 1.82% by weightthoria and having Mo/(Ni-i-Mo)=20.8%. A portion of the alloy powder thusprepared was consolidated by the powder metallurgical techniquesdescribed in Example 1. Examined under the microscope, the product wasfound to be homogeneous with the thoria particles uniformly distributedin the nickel-molybdenum alloy matrix.

Example 3 A batch of 40.7 kg. of nickel carbonate-thoria press cake,made by the procedure of Example 1 but containing about 4% by weightthoria on a metal basis, was repulped with vigorous agitation in 22liters of demineralized water. The slurry thus formed was treated with6.0 liters of ammonium molybdate solution containing 772 grams ofmolybdenum. Over a period of 4 hours, 2.265 liters of concentratednitric acid were added. The pH of the slurry was 6.5 during the last 3hours of this 4 hour period. The slurry was filtered at the conclusionof this time and 32 liters of filtrate contained 46.7 grams molybdenum.This represented a yield of 93.95% of molybdenum values. The pressedcake was dried, calcined, pulverized, and reduced according to theschedule described in Example 1. The alloy powder product, weighing 9.2kg, contained 3.95% ThO and 7.29% Mo/Ni-l-Mo. Powder metallurgicaltechniques applied to this powder produced massive metal which washomogeneous, with thoria particles evenly distributed in thenickel-molybdenum matrix.

Example 4 A 37.3 kg. quantity of washed nickel carbonate-thoria presscake, was prepared by precipitating a solution of nickel nitrate andthorium nitrate with ammonium carbonate solution at pH 7.0 to form aslurry, the solids content of which was about 2% thoria on a metalbasis. This nickel carbonate-thoria press cake was repulped in 30 litersof demineralized water with vigorous agitation. The slurry was treatedwith 3.76 liters of solution containing 510 grams of molybdenum asammonium molybdate, and was afterwards acidified to 6.5 pH by theaddition of concentrated nitric acid. The acid was added over a periodof 4 hours; the pH value of 6.5 was maintained during the final twohours of acid addition. The 37.3 liters of filtrate contained 0.966grams of molybdenum per liter or a total of 36.0 grams of molybdenum;therefore the yield of molybdenum values deposited with the press cakewas 92.94%.

The press cake was dried, calcined, pulverized, and reduced according tothe schedule of Example 1. The alloy powder weighing 8.5 kilograms,contained 1.95% thoria; Mo/ (Ni-l-Mo) 5.30%. Powder metallurgicaltechniques applied to this powder produced massive metal which washomogeneous, with thoria particles uniformly distributed in the alloymatrix.

Example 5 In this example of the operation of this invention, a portionof the filtrate which was obtained after the washing of nickelcarbonate-thoria precipitate was used to dissolve ammonium molybdate andthis solution was pumped through the nickel carbonate-thoria filter caketo effect deposition of the molybdenum values on the precipitate. Thusthe eifect of dispersion of the precipitated particulate solid in theammonium molybdate solution was achieved by circulating the solutionwith respect to the solid particles, rather than circulating theparticles in the solution as in Examples 1 to 4. These two practices areequivalent.

A nickel carbonate-thoria slurry containing 3.18 kg. of nickel values,prepared according to the procedure given in Example 1, was pumped to asmall, recirculating filter press and washed clean. After the last washwater was discarded, 15.0 liters of fresh demineralized water was addedto the system and recirculated through the filter press. A portion ofthe recycle water was used to dissolve ammonium molybdate equivalent to265 grams molybdenum. The ammonium molybdate solution was re-added tothe recycle stream. The recycle stream turned light green as the freeammonium ion redissolved some of the Ni values from the press cake. Overa period of 4.33 hours a total of 0.725 1. of concentrated nitric acidwas added to the recycle stream. A pH value of 6.5 was maintained in therecycle stream over the final 3.5 hours of this acid addition period. Atthe conclusion of the 4.33 hours of recirculation of the filtratethrough the press cake, the cake was filtered to dryness. The filtratewas analyzed and found to contain 1.72 g./l. Mo and 5.65 g./l Ni. Thisrepresents a yield of 90% on the molybdenum values and of 97.21% on thenickel values. The product was found to be 809410.173 Mo/(Mo+Ni), byanalyses of nine samples.

The press cake was dried, calcined, pulverized, and reduced according tothe procedure given in Example 1. Powder metallurgy techniques appliedto this powder produced massive metal which was homogeneous, the thoriaparticles being uniformly distributed in the nickel-molybdenum-matrix.

Example 6 To show the effect of the pH value on the yield of molybdenumand of nickel values which may be obtained by the process of thisinvention, the following example was carried out.

Typical nickel carbonate-thoria press cake, prepared as given in Example1 above, containing 2.2% thoria by weight on a metal basis, was dried at150 C. to produce a light green solid which analyzed 47.5% nickel. Thisdried material was pulverized in a hammer mill and a batch of 190 gramsof the pulverized green cake was slurried with 435 cc. solutioncontaining 10.0 grams molybdenum as ammonium molybdate. The pH of theslurry initially was 7.75. Using 50 cc. of 2 N nitric acid, the pH wasadjusted to 7.0 with vigorous agitation. The agitation was continued for1 hour with the addition of 13 cc. more of 2 N nitric acid to maintainthe pH value at 7.0. The slurry was filtered and the filtrate (285 cc.)was found to contain 5.28 grams of molybdenum per liter, and 1.79 gramsof nickel per liter. This represents a yield of 85% on the molybdenumvalues, and of 99.5% on nickel values,

present and available in the slurries.

A similar run was made with the exception that pH was adjusted to 6.0and held at this value for 1 hour. This experiment yielded a filtratewhich contained 1.83 grams molybdenum per liter, and 11.68 grams nickelper liter. This represented a yield of 94.8% on molybdenum values, and96.8% on the nickel values available in the slurries. Thus it is shownby this example that the molybdenum values deposited with the press cakeincreased and the nickel values decreased as the pH is decreased from7.0 to 6.0, but in either case the yields are economically practicable.

Example 7 This example shows that molybdenum values may be depositedupon calcined Ni-ThO press cake. The deposition of such values, however,occurs quite slowly, even when the pH value is kept near the lower endof the permissible range of 5.5 to 8.5.

A nickel carbonate-thoria press cake was prepared as described inExample 1. This cake was dried, calcined, and pulverized to produce afine black powder which upon analysis was found to be 73.5% nickel. A24.5

. gram portion of this oxide (representing 18 grams of nickel) was mixedwith 100 cc. of water containing 2.0 grams of molybdenum as ammoniummolybdate. The slurry was shaken on a mechanical shaker for a period ofhours. The pH of the slurry after this agitation was found to be 5.95.The slurry was filtered and the filtrate analyzed to show 4.05 grams ofmolybdenum per liter. This represents a 79.7% transfer of the molybdenumvalues to the solid phase.

A similar treatment, but shaken on the mechanical shaker for only 1 hourinstead of 15 hours, had a final pH value of 5.5, and resulted in asupernatent solution containing 10.83 grams of molybdenum per liter.This corresponds to a transfer of only 45.8% of the molybdenum values tothe solid phase. Thus it is shown that molybdenum values can betransformed from ammonium calcined cake, place quite slowly even atExample 8 This example illustrates the preparation of anickeliron-molybdenum-zirconia alloy according to a process of thisinvention.

A slurry of intimately mixed nickel carbonate-ferric hydroxide-zirconiawas prepared by mixing 30 liters each of the following:

(1) Three molar ammonium carbonate, (2) a solution 2 molar in nickelnitrate, and 0.67 molar in ferric nitrate, and (3) a zirconia aquasolcontaining g. ZrO so that the product contained 2.0% zirconia on a metalbasis, calculated on yield of metal values and 100% yield of zirconia.

The slurry thus obtained was filtered, and washed until the filtrate wascolorless. The filtered cake was reslurried in two thirds of its ownweight of demineralized water. To this slurry was added 3.5 liters of asolution containing 250 grams of (NH Mo O '4H O. The pH was adjusted to7.0 using concentrated nitric acid, and was held at that value, whileagitating, for four hours, after which the slurry was filtered. Theproduct was dried, calcined at 450 C. and pulverized. It was reduced ina flow of hydrogen at a maximum temperature of 850 C. for a period of 11hours to produce a metallic powder. The product containednickel:iron:molybdenum in the weight ratio of 27:9:4 with 1.8% zirconiadispersed uniformly throughout the alloy matrix.

I claim:

1. In a process for producing an alloy in powder form, said alloycomprising (A) molybdenum, (B) at least one other metallic componentselected from the group consisting of (I) iron, (II) cobalt, (III)nickel, (IV) chromium, (V) at least one metal of these four withtungsten, and (VI) at least one metal of said four with copper, and (C)a refractory metal-oxygen component consisting of a refractory oxidehaving an average particle size of 2 to 500 millimicrons and a freeenergy of formation at 1000 C. of at least kcal. per gram atom ofoxygen, which process includes the steps of (1) preparing a particulatesolid comprising a compound of each metal other than molybdenum to bepresent in the final alloy, said particulate solid being furthercharacterized in that, after calcination at to 550 C., the said metalcompounds therein are reducible to their component metals at 450 to 1200C., and said particulate solid having so dispersed therein as to beinseparable by mechanical means, from 0.05 to 10% by volume of a saidrefractory metal-oxygen component, (2) depositing amolybdenum-containing coating on the surface of the particulate solidfrom a solution containing a molybdenum compound, (3) separating thecoated solid from the solution and calcining it at from 100 to 550C. and(4) heating the calcined product at 450 to 1200 C. in contact with areducing agent selected from the group consisting of hydrogen, carbon,carbon monoxide, and hydrocarbon gases, whereby the particulate solidand its molybdenum-containing coating are reduced to their componentmetals and these metals are homogeneously alloyed with each other, whilethe refractory metal-oxygen component remains unreduced and uniformlydistributed therein the improvement which comprises effecting thedeposition of step 2 by dispersing the particulate solid of step 1 in anaqueous ammonium molybdate solution having a pH in the range of 5.5 to8.5, in an amount substantially exceeding the solubility of said solidin said solution, and maintaining the pH in that range until themolybdenum-containing coating has deposited on the surface of theparticulate solid.

2. A process according to claim 1 wherein the particulate solid of step1 comprises a compound of nickel.

3. A process according to claim 1 in which the pH of the ammoniummolybdate solution in step 2 is maintained at 6.5 to 7.5.

4. A process according to claim 1 in which the particulate solid of step1 comprises a nickel compound and the refractory metal-oxygen component(C) cornprises thoria.

1 2 References Cited UNITED STATES PATENTS 3,085,876 4/1963 Alexander etal 75-O.55 3,150,443 9/1964 Alexander et al 29-4825 DAVID L. RECK,Primary Examiner. W. W. STALLARD, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,382,062 May 7, 1968 Dale M. Hiller It is hereby certified that errorappears in the above numbered patent requiring correction and that thesaid Letters Patent should read as corrected below.

Column 1, line 13, "modybdenum" should read molybdenum line 55, "ther"should read their Column 4 line 54 "agent" should read reagent ..C0lumn5, line 38, after "preferred" insert reducin Column 7, line 24, "(90C.)"should read (900 C.) line 29, "decanted" should read decanned samecolumn 7, TABLE 1, third column, line 4 thereof, ".0" should read 1.0

Signed and sealed this 7th day of October 1969.

(SEAL) Attest:

EDWARD M. FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting OfficerCommissioner of Patents

